Separation of gases by means of mixed matrix membranes

ABSTRACT

A fluid feed mixture, either liquid or gaseous in nature, may be subjected to a gas enrichment separation process. The process is effected by contacting the mixture with the upstream face of a mixed matrix membrane which comprises an organic polymer having a solid particulate adsorbent incorporated therein, the permeability coefficient of the organic polymer being compatible with the permeability coefficient of the adsorbent. The permeate which emanates from the downstream face of the membrane comprises a fluid product mixture in which the proportion of the first fluid component of the feed mixture, which possesses a greater steady state permeability in relation to the second fluid component, is greater than the proportion present in the original fluid feed mixture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 158,818, filed Feb. 22,1988 and now abandoned which is a continuation-in-part of our copendingapplication Ser. No. 858,321 filed May 1, 1986 and issued as U.S. Pat.No. 4,740,219, which is a continuation-in-part of application Ser. No.697,990 filed Feb. 4, 1985, now abandoned, which is acontinuation-in-part of application Ser. No. 449,042 filed Dec. 13,1982, now abandoned, all teachings of which are incorporated herein byreference thereto.

BACKGROUND OF THE INVENTION

The present invention relates to separation processes and in particularto the use of a mixed matrix membrane combination to achieve suchseparation as well as to the preparation of such a combination and thecomposition of said composition.

DESCRIPTION OF THE PRIOR ART

In recent years, polymeric membranes have attracted a great deal ofinterest for use in gas separation. For example, some membranes whichare used would include silicone membranes for oxygen/nitrogenseparation, cellulose acetate membranes for carbon dioxide removal fromnatural gas and silicone-coated polysulfone membranes for hydrogenrecovery from various waste streams. In a typical operation, a pressuredifferential is maintained across the polymeric membrane and providesthe driving force for the permeation. Two properties of the membrane areof critical importance in determining the performance characteristicwhich is possessed by the membrane. The first property is the solubilityof the gas in the membrane while the second property is the diffusivityof the gas in the membrane material. The product of these twoproperties, that is, solubility and diffusivity, is called thepermeability. The higher the membrane permeability factor, the moreattractive is the use of membranes for a gas separation process. As willhereinafter be shown in greater detail, the permeability of a polymericmembrane may be increased as well as altered by forming a mixed matrixmembrane and thus providing a novel membrane of this invention.

With respect to some of the gas separation membranes heretofore known,it is taught in U.S. Pat. No. 4,243,701 to Riley et al. that certainmembranes may also be utilized for the separation of various gases. Theseparation of a gas mixture utilizing a membrane is effected by passinga feed stream of the gas across the surface of the membrane. Inasmuch asthe feed stream is at an elevated pressure relative to the effluentstream, a more permeable component of the mixture will pass through themembrane at a more rapid rate than will a less permeable component.Therefore, the permeate stream which passes through the membrane isenriched in the more permeable component while, conversely, the residuestream is enriched in the less permeable component of the feed.

The use of adsorbents such as zeolites and silicalite in separatingcomponents from fluid mixtures is also long known. In the adsorptiontype separation process the adsorbent exhibits selectivity of onemixture component over another. Zeolites are hydrophilic crystallinealuminosilicates.

Silicalite, a particular zeolite, is a hydrophobic crystallinesilica-based molecular sieve which has been developed and patented (seeU.S. Pat. No. 4,061,724 to Gross et al). A detailed discussion ofsilicalite may be found in the article "Silicalite, A New HydrophobicCrystalline Silica Molecular Sieve"; Nature, Vol. 271 Feb. 9, 1978,incorporated herein by reference.

Adsorptive separation processes such as those using zeolites are verydifferent from membrane processes. In the typical adsorption process, agas mixture is allowed to come to equilibrium with the adsorbingmaterial and the solid adsorbent thus concentrates the desired gascomponent. A separate step such as heating the adsorbed phase or passinginert gas over the adsorption bed is required to remove and collect thedesired gas component. Hence, an adsorption process requiring distinctadsorption and desorption steps is very different from a membraneprocess and, in general, there is no correlation between materials whichare useful in adsorptive processes and those used for membraneprocesses.

There are numerous references which disclose the incorporation ofvarious materials within separation membranes. U.S. Pat. Nos. 3,457,170to Havens; 3,878,104 to Guerrero; 3,993,566 to Goldberg et al; 4,032,454to Hoover et al; and 4,341,605 to Solenberger et al teach the use ofstructural supports or reinforcement fibers or fabrics to aid themembrane in resisting the high pressures used in the reverse osmosisprocess. U.S. Pat. No. 3,556,305 to Shorr shows a "sandwich" typereverse osmosis membrane comprising a porous substrate covered by abarrier layer, in turn covered by a polymer or film bonded to thebarrier layer by an adhesive polymeric layer. U.S. Pat. No. 3,862,030 toGoldberg shows a polymeric matrix having an inorganic filler such assilica dispersed throughout which imparts a network of micro-voids orpores of about 0.01 to about 100 microns, capable of filteringmicroscopic or ultrafine particles of submicron size. U.S. Pat. No.4,302,334 to Jakabhazy et al discloses a membrane "alloy" comprising ahydrophobic fluorocarbon polymer blended with polyvinyl alcohol polymerwhich imparts hydrophilic properties to the membrane.

The incorporation of particular moleculae sieves into polymericmembranes is also disclosed in the art. In the article "The DiffusionTime Lag in Polymer Membranes Containing Adsorptive Fillers" by D. R.Paul and D. R. Kemp, J. Polymer Sci.; Symposium No. 41, 79-93 (1973),the specific mixed matrix membrane used was a Type 5A (Linde) zeoliteincorporated with a silicone rubber matrix. The Paul et al articleillustrates that the zeolite "filler" causes a time lag in reachingsteady state permeation of the membrane by various gases due to theadsorption of the gases by the zeolite. It is taught in this articlethat once the zeolite becomes saturated by the permeating gas a steadystate rate of permeation through the membrane is reached resulting insubstantially the same selectivity as if the zeolite was not present.

In addition to the aforementioned references, U.S. Pat. No. 4,340,428discloses a semi-permeable asymmetrical membrane which is useful for thedesalination of water utilizing a reverse osmosis process. The membranewhich is used for this purpose comprises a cellulose acetate polymerwhich has incorporated therein a swelling medium consisting of anorganophilic bentonite. However, the reference does not maintain that achange in salt rejection is accomplished by the presence of thebentonite. The patent states that the long-chain hydrocarbon modifiedbentonite, which is employed as a swelling agent, serves as thisswelling agent due to the "dispersion of the hydrocarbon chains, duringwhich the clay mineral flakes increasingly separate from one another,putting into effect the process of gelling or swelling of theorganophilic bentonite". This organophilic bentonite is present only forthe purpose of affecting a resistance to compaction of the membrane. Thesalt rejection performance of the membrane which is accomplished is thatof a pure cellulose acetate membrane rather than a change inselectivity. Thus, the objective to be accomplished by the presence ofthe organophilic bentonite is to obtain a stable membrane which does notcompact during the process due to the reverse osmosis pressure which isapplied to the system during the desalination of the water.

U.S. Pat. No. 2,924,630 discloses a process for fluid diffusionfractionation which utilizes an aluminosilicate for the separation ofgases or liquids. The aluminosilicate barrier which is used ismaintained in either the form of a filter cake on one surface of apermeable solid support or it may be mechanically depressed into ordispersed in the pores of a fluid permeable material. The supportingmaterials will comprise porous supports made from certain plastics suchas casting resins, sintered metals, ceramic-type materials such asAlundum, aloxite and the like. The metals or casting resins are used asa binder which holds one particle of the aluminosilicate to another.This separator, the steady state permeability of the alumino silicate,has not been altered by the porous support as occurs in the presentinvention. Therefore, the materials which act as supports serve merelyas physical supports for the adsorbent while still permitting the fluidto pass therethrough.

U.S. Pat. No. 2,924,630 also teaches use of a solidifiable material suchas a casting resin, a molten metal or other material which is allowed toharden to cover a single layer of the zeolite silicate which ispositioned between the elements of wire or other reinforcing mesh. Theresinous matrix material which is exemplified must be ground away inorder to expose both the upper and lower surfaces of the adsorbent,which is in contrast to the present invention, as hereinafter more fullydescribed, which does not require that the surface of the adsorbent beexposed to the liquid which is being subject to separation. It is to benoted, the patent teaches that the transport of the gas or liquid ismerely through the zeolite crystal and not through the binder. Thiscomposite is not a mixed matrix membrane due to the single phasetransport of the material through the barrier which is in contrast tothe type of mixed matrix membrane which forms the basic of the presentinvention. If one were to look at the teachings of U.S. Pat. Nos.4,340,428 and 2,924,630 in combination, a person skilled in the artwould be led away from the teachings we have now discovered.

U.S. Pat. No. 3,246,767 discloses fluid-permeable materials comprising aporous base having superimposed thereon a microporous layer whichimpregnates the base, said base comprising a fibrous material of which aproportion of fibers extend outwardly from the porous base. This patentdoes not teach a solution cast membrane such as that which is utilizedin the present invention which includes a particulate adsorbent. Incontradistinction to this, the patent discloses a material comprised ofa multitude of fibers attached to a porous base in which the fibers maybe employed together with particulate materials. Likewise, U.S. Pat. No.4,344,775 discloses the use of silicalite as an adsorbent in a gas-vaportreating mat comprised of glass fibers intermixed with micro-bits of anexpanded thermoplastic polymer and an organic bonding agent.

In addition to this patent, other references such as U.S. Pat. No.4,061,724 and the article by Flanigen in Nature, Volume 271, which werepreviously mentioned, teach that silicate may indeed serve as anadsorbent for use in selectively adsorbing organic materials from water.However, these references are silent as to the use of silicalite inconjunction with a solution cast semipermeable membrane of the presentinvention. Indeed, these references teach away from the use of anadsorbent in the separation of gases inasmuch as the references focusspecifically on the separation of organic compounds from water.

U.S. Pat. No. 4,061,724 discloses multi-zoned fiber permeators whichcomprise a plurality of selectively permeable hollow fibers which aresuitable for the selective permeation of at least one fluid in a fluidmixture containing at least one other fluid. While this patent disclosesa wide variety of polymers which may be employed in the membrane, it iscompletely silent with regard to the inclusion of an adsorbent materialin the membrane of the present invention.

U.S. Pat. No. 4,344,775 discloses the use of silicalite as an adsorbentin a matte which is comprised of glass fibers intermixed with micro-bitsof an expanded thermoplastic polymer and an organic bonding agent. Thepatent teaches that the silicalite has a very low selectivity for theadsorption of water and a very high preference for the adsorption oforganic molecules smaller than its limiting size, said silicalite beinguseful for the separation of lower alcohols, phenol, pentane and hexanefrom a fluid stream containing the same, even in the presence of water.However, this patent fails to suggest the use of silicalite, or for thatmatter any other adsorbent, with a solution cast semipermeable membraneof the present invention. The use of an adsorbent with such a membraneis contrasted with "gas-vapor treating matte" comprised of glass fibersintermixed with the micro-bits of an expanded thermoplastic resin and abonding agent which is taught in this patent. The patent is totallysilent with regard to the separation of gases but instead seeks topurify the gaseous stream by removing undesirable substances therefrom.

Another U.S. Pat. No. 4,220,535, discloses multi-zoned hollow fiberpermeators which are comprised of a plurality of selectively permeablehollow fibers which are suitable for the selective permeation of atleast one fluid in a fluid mixture containing at least one other fluid.However, while this patent discloses a variety of polymers which can beemployed in the membrane the patent is completely silent with regard tothe inclusion of adsorbent material in the membrane which will alter thesteady state permeability of the membrane.

U.S. Pat. No. 4,243,701 is directed to a method for the preparation of agas separation membrane which comprises a porous support such ascellulose acetate coated with a thin film of a semipermeable membraneformed from a prepolymer such as dimethylsilicon or styrene. However, nomention is made in this patent with regard to the inclusion of anadsorbent within the membrane.

In contradistinction to the prior patents and articles which have beenheretofore discussed, we have now discovered a novel and highlyadvantageous method of preparing a mixed matrix membrane as well as usesfor the membrane for which it is uniquely suitable, such membraneshaving not been disclosed by any of the known art, either alone or incombination. We have also discovered that the mixed matrix membrane,when prepared according to the process of the present invention, isunique in its character inasmuch as the steady state permeability of themembrane has been altered by the inclusion of solid particulateadsorbents thereon, in such a manner so as to permit a desiredselectivity with respect to the passage of a predetermined fluid, andparticularly a gas, from a mixture of fluids or gases through the mixedmatrix membrane. We have further developed a specific combination ofingredients making up a mixed matrix membrane which heretofore has notbeen known prior to our invention.

BRIEF SUMMARY OF THE INVENTION

This invention relates, in one embodiment thereof, to a process for theseparation of a first gas component from a fluid feed mixture whichcomprises a first gas component and a second gas component by contactingthe aforesaid gas feed mixture with the upstream face of a mixed matrixmembrane which consists of an organic polymer having a solid particulateadsorbent incorporated therein, and recovering a permeate in which thefirst gas component of the gas feed mixture is present in a greaterproportion than was present in the gas feed mixture.

Another feature of the present invention is method of manufacture of amixed matrix membrane comprising adsorbent particles incorporated with amembrane material, the method comprising: (a) forming a slurry of theadsorbent particles in a solvent in which the membrane material issoluble; (b) thoroughly stirring the slurry so as to obtain a highlyuniform dispersion of the particles in the solvent; (c) adding themembrane material to the slurry while continuing to stir the slurryuntil a suspended homogeneous solution is obtained; and (d) casting thesolution to obtain said mixed matrix membrane.

In addition, a supplemental feature of the present invention is a mixedmatrix membrane which has been prepared according to the methodherein-before set forth.

It is therefore an object of this invention to provide a process forseparating various components of a gas feed mixture either liquid orgaseous in nature by utilizing a mixed matrix membrane.

In one aspect, an embodiment of this invention is found in a process forthe separation of a first gas component from a gaseous feed mixturecomprising a first gas component and a second gas component bycontacting, at separation conditions, said mixture with the upstreamface of a solution cast mixed matrix membrane consisting of an organicpolymer selected from the group consisting of polycarbonates,polyamides, polysulfone and polysilicone having a solid particulateadsorbent incorporated therein, the steady state permeability of saidmixed matrix membrane being different than the steady state permeabilityof said organic polymer, said first gas component having a greatersteady state permeability than said second gas component, and recoveringafter said contacting, a permeate which comprises gaseous productmixture in which the proportion of said first gas component to saidsecond gas component is greater than the proportion of said first gascomponent to said second gas component in said gaseous feed mixture.

Other objects and embodiments will be found in the following furtherdetailed description of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As hereinbefore set forth, the present invention is partially based onthe aforementioned art concerning membranes, particularly membranescomprising polymeric organic materials. The present invention alsoutilizes one or more of the well-known adsorbents such as zeolites,silicalite, activated carbon or ion-exchanged resins. The presentinvention, however, in a manner not known to the art, provides a mixedmatrix membrane by incorporating the absorbent with a polymeric organicmaterial which forms a membrane to create the desired composite in whichthe steady state permeability of the mixed matrix membrane differs fromthe steady state permeability which was possessed by the polymericorganic material, and uses that creation in a unique process forseparating fluid components such as gases from each other in a mannerwhich would otherwise be difficult or impossible to effect theseparation.

Those skilled in the art of membrane separation technology know thatdifferent components of a fluid system may pass through a properlyselected membrane at different rates due to different diffusivity andsolubility characteristics (hereinafter collectively referred to as"permeability") of each component in the membrane. This phenomenon maybe expressed in terms of a separation factor as defined in the formula:##EQU1## where A/B=separation factor;

(C_(A) /C_(B))P=concentration of component A--concentration of componentB in the permeate phase (emanating from the downstream face of themembrane);

(C_(A) /C_(B))R=concentration of component A--concentration of componentB in the raffinate phase (at the upstream face of the membrane).

The higher the separation factor, the better the separation that will beachieved. An A/B of over 3.0 is considered conducive to an excellentseparation.

We have made the discovery that when a properly selected adsorbent isincorporated with a particular membrane in a certain manner to obtain amixed matrix membrane, a surprising and unexpected increase will occurwith regard to the separation factor of that membrane for a given fluidmixture. This difference in separation factor is due to the alterationin steady state permeability which has been imparted to the mixed matrixmembrane in contrast to the steady state permeability of the organicpolymer. We have thus obtained by our discovery a viable process inwhich fluid components, and particularly gases, may be separated from amixture because of the marked differences in their respectivepermeabilities through the mixed matrix membrane, which markeddifferences do not occur in an adsorbent-free membrane. Furthermore, incontradistinction to the teachings of the above Paul et al article, wehave discovered that proper selection of an adsorbent and membranematerial for a given system will enable long term steast statepermeation with a corresponding selectivity of desired fluids such asgases through the mixed matrix membrane to be achieved as opposed to thetrivial short term effect noted by Paul et al.

The mixed matrix membrane which is prepared according to the process ofthe present invention, will possess the ability to effect the separationof various components of a fluid, and particularly a gaseous, feedmixture by utilizing the steady state permeability characteristic ofeach component of the mixture. The desired effect is achieved byincorporating an adsorbent of the type hereinafter set forth in greaterdetail with certain polymeric materials, the permeability coefficient ofthe polymer being compatible with the permeability coefficient of theadsorbent, the two permeability coefficients preferably being within anorder of magnitude of one to the other. By utilizing such a combination,it is possible, as will hereinafter be shown in greater detail, to alterthe separation factors of polymeric materials as well as to provide adesired selectivity factor which is not found in all mixed membranes.

The mixed matrix membranes of our invention comprise certain organicpolymer materials having a solid particulate adsorbent incorporatedtherein. The mixed matrix membrane of our invention will comprise anadsorbent incorporated in certain organic polymer materials. In thepreferred embodiment of the invention, the organic polymer material willbe selected from the group consisting of polysulfones, polycarbonates,polyethers, polysilicones and polyamides. The solid particulateadsorbent material which is incorporated in the aforesaid organicpolymers will be selected from the group consisting of zeolites such ascrystalline aluminosilicates, silicalite, inorganic oxides, activatedcarbon or an ion-exchange resin. The selection of ingredients for themixed matrix membrane will depend on the feed mixture from which thecomponents are to be separated. For example, the feed mixture may be aliquid or a gas; in the latter case we have found a mixed matrixmembrane comprising silicalite (preferably from about 5 wt. % to about25 wt. %) incorporated with a polysilicone will have a utility,particularly in separating oxygen from nitrogen or carbon dioxide fromhydrogen. In those two separations, oxygen and carbon dioxide,respectively, are the more permeable gases.

The performance of the mixed matrix membrane of the present invention isparticularly surprising and unexpected in view of the unpredictabilityof steady state separation factors which are inherent in variousadsorbent-membrane systems. For example, when attempting to separatecarbon dioxide from hydrogen, it is known that hydrogen has a greaterpermeability through a plain cellulose acetate membrane as has beenshown in prior references and, on the other hand, that silicalite has agreater adsorptive affinity for carbon dioxide. There is no way that aperson skilled in the art could have predicted from this knowledge thata steady state separation process could be achieved when utilizing amixed matrix membrane comprising cellulose acetate having silicalite asthe solid particulate adsorbent incorporated therein, whereby a permeatestream enriched in carbon dioxide could be obtained and with thesilicalite not simply becoming saturated with carbon dioxide and ceasingto influence the separation of carbon dioxide from hydrogen.

The above example with regard to the separation of carbon dioxide andhydrogen readily illustrates the unexpected results which are obtainedby utilizing a mixed matrix membrane in which the steady statepermeability of the mixed matrix membrane has been altered with respectto the steady state permeability of the organic polymer, this being inconjunction with the corresponding alteration of the steady stateselectivity of the components with respect to the passage of theparticular fluid component (either gas or liquid) through the mixedmatrix membrane. However, as will hereinafter be shown in greater detailby comparable examples, this phenomenon is only noticeable when theadsorbent which is incorporated into the organic polymeric membranepossesses a permeability coefficient which is compatible with thepermeability coefficient of the polymer.

The separation of the two or more components of a fluid feed mixture,such as a mixture of gases, according to the process of the presentinvention when utilizing the novel mixed matrix membranes may beeffected over a wide range of separation conditions. For example, theseparation may be effected when utilizing ambient temperatures (20°-25°C.) and a pressure which may be in the range of from about 69 kPa toabout 3447 kPa (10 to 500 psig) on the upstream phase of the mixedmatrix membrane. The flux, or rate of permeation, through the membraneis directly proportional to the pressure differential across the face ofthe membrane.

Another aspect of our invention is the novel and highly advantageousmethod that we have discovered to make mixed matrix membranes. In itsbroadest embodiment, the method involves forming a slurry of solidparticulate adsorbent particles in which the membrane material issoluble, thoroughly mixing the slurry to obtain a highly uniformdispersion, adding the membrane material to the slurry while continuingto mix until a suspended homogeneous solution is obtaned and casting thesolution to obtain the mixed matrix membrane. We have found adding thesolid particulate adsorbent particles to the solvent prior tointroduction of the membrane material to be very important from thestandpoint of the quality of the mixed matrix membrane ultimatelyobtained, i.e., the freedom of the membrane from air pockets andperforations. In contradistinction, the Paul et al article teaches atpage 85 to disperse the molecular sieve particles directly into theprepolymer. We believe that the solvent serves to drive air out of thepores of the adsorbent so that when the membrane material is added therewill be no air to form pockets and pinholes.

The constant mixing as mentioned in the above method is also veryimportant. Mixing will, of course, facilitate a uniformity of thedispersion of the adsorbent particles in the membrane, and in minimizingthe clumping together of the particles will further preclude theformation of pinholes. Mixing is best effected by ultrasonic means.

The membrane material, in which the adsorbent is incorporated, deemedmost likely for use in the method of the present invention, comprises anorganic polymer of the type hereinbefore mentioned which may be employedto form the membrane material, and that the particular polymer andsolvent which are utilized to form the casting solution will bedependent upon the particular polymer which is employed.

The casting of the solution as mentioned in the above method ispreferably effected, at least when the membrane material comprises anorganic polymer, by (a) pouring the solution onto a flat surface; (b)slowly removing substantially all of the solvent from the solution so asto cause gelation of the solution and formation of a membrane; (c)submerging the membrane in a hot liquid bath to cause the annealing ofthe membrane; and (d) drying the membrane. Under certain circumstancesthe solvent is removed solely by evaporation, e.g. when using a siliconeas the membrane material and Freon as the solvent. However, under othercircumstances, a portion of the solvent may be removed by evaporationfollowed by submerging the partially formed membrane in a liquid bath inwhich the solvent is soluble, e.g., a polysulfone as the membranematerial, acetone or N,N'-dimethylformamid as the solvent and ice wateras the bath liquid. Annealing, on the other hand, might be carried outin a hot water bath at a temperature of from about 50° C. to about 100°C. It is believed that annealing causes the polymer chains comprisingthe membrane material to line up in a parallel manner rather than crossover each other which serves to further minimize the creation ofundesirable voids.

The following examples are presented for purposes of illustrating amethod for preparing a mixed matrix membrane of the present invention aswell as the use thereof in effecting a separation of two components of afluid feed mixture.

EXAMPLE I

A mixed matix membrane of about 30 microns in thickness was prepared inaccordance with the method of the present invention by the followingsteps:

1) 2.5 grams of silicalite powder was stirred by ultrasonic means in 15grams of a solvent comprising Freon TF at room temperature for about 3hours;

2) 11.1 grams of a mixed silicon was added to the silicalite-Freonsuspension, the suspension was stirred until a suspended homogeneoussolution was obtained with a partial vacuum being applied for a shortperiod of time in order to ensure the removal of all air bubbles;

3) The solution was poured on the top horizontal surface of a cleanglass plate and a portion of the Freon was allowed to slowly evaporate;

4) After drying, the membrane was cured at a temperature of 82° C. for aperiod of 1 hour.

EXAMPLE II

A piece of the mixed matrix membrane which had been prepared accordingto the method described in Example I was cut to an appropriate size andused in a test cell to determine the ability of the membrane to separateoxygen from nitrogen. The upstream face of the membrane was exposed toair and a differential pressure of 1034 kPa (150 psig) was maintainedacross the membrane. The gas emanating from the downstream face of themembrane, i.e., the permeate, was analyzed and analysis disclosed thatthe separation factor (αO₂ /N₂) was 2.14.

EXAMPLE III

In a manner similar to that set forth in the above examples, 2 grams ofboehmite, 0.4 grams of silicon RTV 615B and 3.7 grams of silicon RTV615A were mixed in 40 grams of Freon TF. The mixed matrix membrane whichwas formed by casting the solution on a glass plate and curing at atemperature of 82° C. for one hour was cut to an approximate size andused in a test cell to determine the ability of the membrane to separateoxygen from nitrogen. The upstream face of the membrane was exposed to afeed mixture of air while maintaining a differential pressure of 1034kPa (150 psig) across the membrane. The gas emanating from thedownstream face of the membrane was analyzed and it was found that thecalculated separation factor was 2.19.

EXAMPLE IV

In this example, a membrane was prepared by admixing 1.1 grams ofsilicone RTV 615B and 10 grams of silicone RTV 615A in 15 grams of asolvent comprising Freon TF. The casting solution which contained noadsorbent such as silicalite or boehmite was cast on a glass plate andcured at a temperature of 82° C. for one hour. The permeation test ofthis membrane utilizing a feed mixture comprising air disclosed acalculated separation factor of 2.03.

EXAMPLE V

A mixed matrix membrane was prepared by stirring 2.5 grams ofgamma-alumina in 40 grams of acetone at room temperature for about threehours utilizing ultrasonic means to accomplish the stirring. Followingthis, 10 grams of cellulose acetate which possessed an acetyl content of39.8% was added to the suspension of alumina in acetone, the suspensionwas stirred until a suspended homogeneous solution was obtained whileapplying a partial vacuum for a short period of time to ensure removalof all air bubbles. The resulting solution was poured on the tophorizontal surface of a clear glass plate and a portion of the acetonewas allowed to slowly evaporate until a film had formed on the uppersurface of the solution. The thin film membrane was allowed to set for aperiod of two minutes and was then submerged in an ice water bath for aperiod of two minutes. The formed membrane was removed from the icewater bath and submerged in a hot water bath which was maintained at atemperature of 90° C. for a period of one hour. Thereafter, the membranewas dried by placing it between paper towels with a glass plate oneither side as a means for preventing the membrane from curing, followedby placing the membrane in air to effect a complete drying.

A piece of the mixed matrix membrane prepared according to the aboveparagraph was utilized in two permeation tests in a test cell utilizinga test similar in nature to that set forth in the above examples. Thepermeation test using air as the feed stream at a pressure of 1034 kPa(150 psi) disclosed the separation factor (αO₂ /N₂) was 4.33. A secondsample of the membrane was used in a permeation test employing a carbondioxide/hydrogen feed stream at 345 kPa (50 psi). The separation factorfor this test was 2.05±0.47.

EXAMPLE VI

In a manner similar to that set forth in the above examples, 1.2 gramsof a polysulfone may be admixed with a solvent comprisingN,N'-dimethylformamide. After treatment in a manner similar to that setforth in Example I above, 10 grams of a zeolite may be added to thesuspension which is then stirred until a suspended homogeneous solutionis obtained. The solution may then be poured onto a clean glass plateand the Freon allowed to evaporate until a film is formed on the uppersurface of the solution. The membrane is then allowed to set submergedin an ice water bath, followed by submersion in a hot water bath andthereafter dried. The cured membrane may then be used in a permeationtest to separate carbon dioxide from a carbon dioxide/hydrogenfeedstream.

EXAMPLE VII

In this example, 1 grams of a polyamide may be dissolved in a solventcomprising formic acid/methanol and after being stirred for a period ofabout 3 hours, 10 grams of activated carbon may be added to thesuspension. The suspension is then stirred until a suspended homogeneoussolution is obtained and the solution is then poured onto a glass plate.A portion of the formic acid/methanol is allowed to evaporate until athin film is formed on the surface, following which the membrane isdried in a manner similar to that set forth in Example V above. Afterdrying and curing, the membrane may then be used in a permeation test todetermine the ability of the membrane to separate oxygen from nitrogen.

We claim as our invention:
 1. A process for the separation of oxygen andnitrogen from a gaseous feed mixture containing same by contacting, atseparation conditions, said mixture with the upstream face of a solutioncast mixed matrix membrane, consisting essentially of polysiliconehaving a solid particulate adsorbent incorporated therein, the steadystate separation factor for oxygen in nitrogen being increased comparedto the steady state separation factor of a membrane consisting of saidpolysilicone without said solid particulate adsorbent, said oxygenhaving a greater steady state permeability than said nitrogen, andrecovering from the downstream face of said membrane after saidcontacting, a permeate which comprises said oxygen in greater proportionthan said nitrogen.
 2. The process as set forth in claim 1 in which saidseparation conditions include ambient temperatures and a pressure in therange of from about 10 to about 5000 lbs per square inch gauge.
 3. Theprocess as set forth in claim 1 in which said mixed matrix membranecontains from about 5% to about 25% by weight of said solid particulateadsorbent.
 4. The process as set forth in claim 1 in which said solidparticulate adsorbent comprises a zeolite.
 5. The process as set forthin claim 4 in which said zeolite comprises a crystallinealuminosilicate.
 6. The process as set forth in claim 1 in which saidsolid particulate adsorbent comprises a silicalite.
 7. The process asset forth in claim 1 in which said solid particulate adsorbent comprisesan activated carbon.
 8. The process as set forth in claim 1 in whichsaid solid particulate adsorbent comprises an inorganic oxide.
 9. Theprocess as set forth in claim 1 in which said organic particulateadsorbent comprises an ion exchange resin.